1. Field of the Invention
The present invention relates to a gas turbine being provided with a sealing structure preventing combustion gas or a cooling medium from leaking between rotor discs of the gas turbine.
2. Description of the Prior Art
A general construction of a gas turbine is shown in FIG. 8. The gas turbine compresses air in a compressor 51 and subsequently introduces the compressed air to a combustor 52. The combustor 52 generates combustion gas by supplying fuels to the compressed air and introduces the generated combustion gas to a turbine 53. The turbine 53 rotates by the combustion gas, and electric power is produced from a generator 54.
In order to enhance the efficiency of a gas turbine, it is necessary to generate higher temperature combustion gas. Therefore, a cooling medium such as a cooling air or a cooling steam and the like is used for the purpose of cooling of rotating and stationary blades. For an example, a case will be explained hereinafter where a part of the compressed air from the compressor 51 is used as a cooling medium.
FIG. 9 is a cross-sectional view showing the inside of the turbine 53. The turbine 53 is provided with a rotor having a plurality of rotor discs 60 installed around a rotor axis 58. FIG. 10 is a perspective view showing a part of a sealing construction of adjacent rotor discs 60 facing each other. The adjacent rotor discs 60 have an overhang portion 3 (sometimes referred as a “disc land”) formed on the surfaces thereof facing each another. The overhang portions 3 are formed in the form of a ring around the rotor axis 58, projecting to face each other.
The surfaces facing each other at the edge of the overhang portions 3 have a groove portion 4 provided circumferentially. An annular sealing plate assembly 71 is inserted into the groove portions 4 circumferentially. When the rotor discs 60 rotate, the sealing plate assembly 71 is pressed outward in the radial direction of the groove portions 4 due to a centrifugal force.
As a result, the inner surfaces of the groove portions 4 and the outer surface of the sealing plate assembly 71 are attached firmly. Consequently, as shown in FIG. 9, a cooling air 57 being introduced into the inside of the rotor is prevented from flowing out to the gas paths 55 of the turbine 53. Moreover, the combustion gas 56 flowing in from the combustor 52 and passing through the gas paths 55 is prevented from flowing into the inside of the rotor.
A concrete construction of such a sealing plate assembly 71 as described hereinabove is disclosed in Japanese Patent Application Laid-Open No. H11-247999. FIG. 11 and FIG. 12 are a perspective view and a cross-sectional view showing the sealing plate assembly 71, respectively. The sealing plate assembly 71 consists of two-ply sealing plates including an outside sealing plate 74 and an inside sealing plate 75, and a leaf spring 72. A locking pin 73 is firmly fixed to the outside sealing plate 74 by welding. The inside sealing plate 75 is fixed by means of the locking pin 73, thereby preventing circumferential misalignment between the outside sealing plate 74 and the inside sealing plate 75.
In addition, the outside sealing plate 74 and the inside sealing plate 75 are divided into a plural number circumferentially. An annular sealing plate assembly 71 is constructed by having a leaf spring 72 installed to the inside of the inside sealing plate 75. As shown in FIG. 10, the sealing plate assembly 71 being constructed as described hereinabove is inserted into the inside of the groove portions 4 of the overhang portions 3 so as to be assembled to the rotor discs 60.
In the conventional sealing plate assembly 71 as described hereinabove, the outside sealing plate 74, the inside sealing plate 75 and the leaf spring 72 are restrained from mutual relative movement by the locking pin 73. However, because the sealing plate assembly 71 is not fixed to the rotor discs 60, relative movement in an integrated manner is possible inside the groove portions 4.
During steady operation of a gas turbine, the rotor discs 60 are operated at the rated speed. Therefore, the sealing plate assemblies 71 are pressed outward in the radial direction of the groove portions 4 by the centrifugal force and do not make relative movements to the rotor discs 60. When the rotor discs 60 rotate at a low speed, the pressing force due to the centrifugal force is small, which causes such looseness to occur as the sealing plate assemblies 71 make relative movements circumferentially and axially inside the groove portions 4. As a result, there arises a problem that the sealing plate assemblies 71 will get worn or damaged in course of time, which requires a periodical replacement.
Moreover, the sealing plate assembly 71 has the outside sealing plate 74 and the inside sealing plate 75 integrated by the locking pin 73 being fixed firmly to the outside sealing plate 74 by welding. Therefore, in order to replace sealing plate assemblies 71 during a periodical overhaul inspection, it is necessary to bring the main gas turbine body back to a factory to disassemble the turbine. As a result, costs of a periodical overhaul inspection increase and a unit outage period becomes longer, which causes a problem that maintenance costs will further increase.